Volume control



NOV. 24, 1931. F H, BRAKE VOLUME CONTROL Filed July 24, 1929 2 Sheets-Sheet l lflwz n E NF T 1 F, H. DRAKE VOLUME CONTROL Nov. 24, 1931.

Filed July 24, 1929 2 Sheets-Sheet 2' Patented Nov. 24, 1931 i, UNITEnOsTAi-Es lTO RADIO CORPORATION- F AMERICA,

DELAWARE Y V I "PATENT OFFICE FREDERICK BRAKE, j o F rooNroN, NEW .IERSESL ASSIGNOR., BY MESNE ASSIGNMENTS,

OF YORK, N. Y., A CORPORATION OF VOLUME CONTROL -Application filed July 24,

1 itwillfb'e apparent that the novelmethodrof rlifierw .j L The relatively'small collector systems employed on aircraft necessitate the use of a plurality of stagesiof radio frequency amplification,VV andv the :rapidly varying `field strength'encounteredl when the aircraft is in the neighborhoodof the--radiobeacon or transmitter stationcalls `for .-aniextended rangciof'amplificationor volume control.v

VIt has been proposedft'o. control the amplification-.by regulating the filament or,l cathode controhmay be .applied to V.any cascaded 4amheater current supplied to a plurality ofthe cascaded stages, the several `filaments-or cathode'heatersbeingin parallel Witheacli other,

andin series with the source of supply anda commonrresistance. An amplication -control of! this type does lvarythefamplification orloutput volume over an extended rangebut itis :openito the serious objection that it-is commercially impracticable to construct an adjustable resistance which,.lthroughoutl:the

.range `of adjustment of the resistance, will produce equal` or approximately @equal changes iniamplification for a. given angular adjustment of lthecontrol device. In some ranges'of adjustment ofthe control device, lthe change in yamplification AWas relatively q small orsubstantially negligible, while in another range the amplification changed at such a rapid 'raterthatfconsiderable difficulty Was experienced in setting the control device to effect the desired: amplification.

An object ofv thepresent'inventionfis to vprovide a cascaded' amplifierincluding an adjustable resistance common to the-filament or cathodeheater circuitsfof a plurality of stages', and in which'the Achange in amplification, for a given lchange inthe 'setting of the Contact arm ofthe resistance, may be substantially constant throughout the range'of adjustment of the resistance. yA

1929. Serialv No. 380,713.

further object is to provide, in a cascaded amplifier having its filaments fed in parallel lfromva c'ommonsource and through a single adjustable resistance, resistances individual tothe filament circuits of the several audions for lplacing the operating points `of the respective audions upon different ,portions of their gain-filament voltage characteristic. More specifically, an object is to .provide a cascaded amplifier in 4which a resistance is included in the filament circuit of one tube for shifting its operating point to a `portion of the gain-filament voltage characteristic at Vwhich the Slope is substantially different from amplifier that which another' audion of the is Operating.

These and other objects of the invention will bey apparent from the followingidescripf tion, ywhen taken vwith` the accompanying draw-ings in which,

Fig. lisa circuit diagram'of a radio receiver,,embodying` the invention7 y yFig, 2 isyan experimental curve indicating the relationship between stage gain and volume control voltage in a singlestage, and` Fig. 3 comprises curves plotted from experimental datataken with a receiverincluding a two stage radio frequency amplifier embodying the invention, rand the receiver when the .two stage amplifier was provided with a volume control of the previously known type. Y

The circuit diagram of Fig. l illustrates a receiver having two tuned radio frequency stages withtetrodes T, an audion detector l) and two audio amplifying audions A. Except for the circuit elements, shown by the heavier lines, which supply current to the filaments of the radio frequency amplifiers the electrical and mechanical arrangement of the-receiver forms no .part of the present invention. f f v The filaments ofthe amplifiers T areifed, in parallel, from a source ofcurrent such as battery A, and the portion of 'the Supply circuit commento both filaments includes the volume control resistance R, a fixed control gridbias resistance Re, and preferably al fix'edre'sistance R2 which limitsithe maximum of one tube tov a lower. section ofthe charvoltage that may be impressed across the filament circuits.

The circuit arrangement, so far as described, is of conventional form. In accordance with the present invention, a. resistance Haris provided in the filament circuit of only one of the amplifiers toreduce the filament voltage on that `tube below that applied to the other tube.

The effect of' the added resistance R3 will ybe apparent from a consideration of the characteristicv curve shown as Fig.' 2. lThe curve was plotted from data obtained experimentally with a tetrodeof theltype known commercially as UX 222 and represents, for a single radio frequency stage, the variation of amplification with filament voltage. The normal yor 'maximum filament voltage for `tetrodes of this particulartype lis 3.3 volts,

and it is to benoted'that this voltage places the operating point of thetube at ya point A, i. e., past the knee of the curve.

To decrease the amplification of'a single stage,`or aplurality of stages operated under identical "conditions, the voltage control resistance inustbe'turned through asubstantial arc'away from-its maximum voltage (knee Yof the curve)v adjustment before volume control is effected.

By initially shifting the' operatingpoint appreciable acteristic', for example to point B, theamplication of the cascaded stages will be changedr4 at different rates asl the fila-ment 'voltages .on Aall stagesl are simultaneously reduced. l Starting with norinal .or4 maximum overall amplification, as the'resistanc'e. is adjustedto decrease the filament voltages, the gain' ofthe'tube operating at point `B decreases ata comparatively rapid rate while the decrease'for the Itube `operating yat 'point A r-is negligible. As the resistance'i's. ad-

justed-.to vary the amplification of the first tube along the upright portion of thecharacteristic, the change in amplification of the second tube is appreciable but is of a de'- cidedly lower order of magnitude; When the operating point of the second tubey is upon the upright portion of the characteristic, the first tube is operating in the region of lower slope. `By an appropriate choice of the spacing of the operating points, the variation in overall amplification, for a given angular y Fig. l for different valuesV of the added resistance R3. The ordinatesl represent sensitivity on a logarithmic scale and the abscissa indicate angular adjustment ofthe dial of the volume control resistance. y

' By sensitivity is meant the signal strength or inputto. the receiver required for a pre- Y determined constantoutput since the effect upon the Year of agivenv signal varies as the logarithm of input energy, the curves indicate the relationship which 'must' be maintained between control dial setting and signal strength if, for varying signal strength, the

output volume is to` be maintain-ed constant.

Curve C was plottedY from data obtained when the resistance R3 was omitted, andRz and R.,k were 3.6 and 6'. ohms respectively. With these values- .for the fixed resistances,

a 6 vo-lt battery A, and a volume control re- Y sistance adjustable from zero* to 20 ohms, the control dial setting of ?7 placedl the normaloperating potential, 3.3 volts, on the filaments of both tubes. lt will be noted that practically all of thevoliimeV controlfalls within less' thany one-third of ythe keffective operatingV rangeo-f the control dial.

6 ohm resistance was introduced intothe filament circuit of the first tetrode, yas indicated by R3 in Fig. l. This initial shifting ofthe operating point of the first tetrode results in a slight Adecrease vin the sensitivity of the amplifier, i.' e., a .slight reduction in the max-Y inium overall amplification, and. distributes the Acontrol'substantiallyfuiiiformly .over the im:

range ofV adjustment ofthe control device. 1;

-As indicated by curveE, thejnormal operating point .of .one tubek may be shifted `to .a still lower-pointon the curve. VInthisv instance, az 10" ohm resistor.V was .inserted as R3, but this further displacement ofthe nor* mal operating point of one tube substantially decreases the maximunioverall amplification and reduces the effective range of adjustment ofthe controlfdial.v

l While I havedescribed the 'invention' as appliedk to. a two stage amplifier, it is to be understood that the invention is not limited to a volume control based upon any particular number of cascaded stages, Vor to the particular values ofl resistances specified above.

The value of the'resistance Rs'depends, Vof

course upon the type of tube and the num-V ber of stages subjected tovolui'ney control.

W'hen more than two stages are used, .the normal operating points ofthe several stages are displaced 'to fall upon different portions Vof the gain-control vvoltage' characteristic by inserting, in all but one stage, resistances R3 of differentvalues. l

vnrlhev inventionis .equally applicable to triod-e tubes and to tubes employing'separatel heaters forf the cathode.V

Iclaim; Y L l' 1In acascaded amplifier, aplurality of The data of curve'l) was obtained when a` A. audions having substantially identical characteristics, a source of current, circuit ele- Y .ments connecting the filaments of the several audions in parallel with each other and across rsaid current source, an adjustable resistance included in thefilament circuits of all of said Y audions, and a voltage-reducing resistance in the lament circuit individual to one of said audions.

2. rIhe invention as set forth in claim l,

wherein the magnitudes of the resistances are,v

' tially identical audions included in the respective stages, characterized by the fact that lthe filament circuit of one stage includes a resistance which decreases the voltagev across l the filament voltage across the Vtube included the filament of thattube below the value of inanother stage of said amplifier.

,4. In an amplifier, a plurality of cascaded y amplifier' stages including audions ofV substantially identical characteristics, a source of current for ene'rglzing the filaments of all stages, an adjustable resistance 1n series be tween said source and said filament circuits,

and a resistor in the filament circuit of one stage effective to vdecrease the filamentvolt Y age of thatlrs'tageto shift the operating point thereof to a portion of the characteristic curve having a slope differing substantially from that at the operating point of another stage.

5. Ina cascaded amplifier, a plurality of audions, a source of current for heating the cathodes of said audions, an adjustable resistance common to the cathode heating circuits temperatures of both cathodes to lower the amplification of said amplifier.

7. In a` cascaded radio frequency amplifier, a plurality of electron discharge tubes, a source of current for energizing the cathodes of said tubes to emit electrons, an adjustable resistance common to the cathode energizing circuits of all of said tubes, and an impedance in the energizing circuit of the first of said tubes and of such magnitude that the operating electron emissivity of the cathode of that tube is reduced below the point corresponding to maximum amplification when the said adjustable resistance has such effective value that the cathode of a following tube has an emissivity effective to give maximum amplification.

8. In the operation of a cascaded radio frequency amplifier, the method of effecting amplification control by simultaneous adjustment of the electronic emissivity of the cathodes of the tubes included in the amplilier, which comprises initially adjusting the amplifier for maximum amplification by decreasing the electron emission of the cathode of at least one of the tubes to a point corresponding to less than maximum amplification `of that tube while operating the ycathode of at n least another tube with electron emission giving rise to approximately maximum amplifi-r cation, and simultaneously reducing the electron emission of both cathodes to lower the amplication of said amplifier.

In testimony whereof, I affix my signature.

FREDERICK I-I. DRAKE.

of all of said audions, and a resistance in the f l y heating circuit of one audion and of such magnitude that the operating temperature of j the cathode of that'audion is reduced below the point corresponding to maximum amplification when thesaid adjustable resistance has such effective value that the cathode of another audion has a temperature effective to give maximum amplification.

'6. In' the operation of a'cascaded audion amplifier, the method of effecting amplification controlrby simultaneous adjustment of the temperatures of the cathodes of the audions included in said stages, which comy prisesinitially adjusting the amplifier for 1 maximum amplification by decreasing the temperature Vof Aone audion cathode to a point corresponding to less than maximum amplification of ythat audion while operating the cathode of another audion 'at a temperature giving rise to approximately maximum amplification, and simultaneously reducing the sov 

